Streaming media is multimedia that is constantly received by, and normally presented to, an end-user (using a client) while it is being delivered by a streaming provider (using a server). One problem with existing media streaming architectures is the tight coupling between server and client. A stateful connection between client and server creates additional server overhead, because the server tracks the current state of each client. This also limits the scalability of the server. In addition, the client cannot quickly react to changing conditions, such as increased packet loss, reduced bandwidth, user requests for different content or to modify the existing content (e.g., speed up or rewind), and so forth, without first communicating with the server and waiting for the server to adapt and respond. Often, when a client reports a lower available bandwidth, the server does not adapt quickly enough, causing breaks in the media to be noticed by the user on the client as packets that exceed the available bandwidth are not received and new lower bit rate packets are not sent from the server in time. To avoid these problems, clients often buffer data, but buffering introduces latency, which for live events may be unacceptable.
In addition, the Internet contains many types of downloadable media content items, including audio, video, documents, and so forth. These content items are often very large, such as video in the hundreds of megabytes. Users often retrieve documents over the Internet using Hypertext Transfer Protocol (HTTP) through a web browser. The Internet has built up a large infrastructure of routers and proxies that are effective at caching data for HTTP. Servers can provide cached data to clients with less delay and by using fewer resources than re-requesting the content from the original source. For example, a user in New York may download a content item served from a host in Japan, and receive the content item through a router in California. If a user in New Jersey requests the same file, the router in California may be able to provide the content item without again requesting the data from the host in Japan. This reduces the network traffic over possibly strained routes, and allows the user in New Jersey to receive the content item with less latency.
Unfortunately, live media often cannot be cached using existing protocols, and each client requests the media from the same server or set of servers. In addition, when streaming media can be cached, it is often cached by specialized cache hardware, not existing and readily available HTTP-based Internet caching infrastructure. The lack of caching limits the number of parallel viewers and requests that the servers can handle, and limits the attendance of a live event. The world is increasingly using the Internet to consume up to the minute live information, such as the record number of users that watched live events such as the opening of the 2008 Olympics via the Internet. The limitations of current technology are slowing adoption of the Internet as a medium for consuming this type of media content.
Many video solutions on the Internet involve the ability to deliver text and data that is synchronized to the video's timeline. For example, the data may include closed captions, captions, advertising insertion, and play-by-play captioning. Existing solutions to this problem have used provisions in media formats that allow custom data to be embedded in the headers, and workflows that use a different mechanism for delivery of the data out-of-band. These solutions do not work well for pull content, where a client regularly requests data from one or more servers. With pull content, the client has to be informed of what content to request, which can be particularly difficult for sparse or sporadic content that is only occasionally included in a stream. Unlike video or audio data, which the client can simply request on a routine schedule (e.g., every two seconds), sparse data such as an advertisement may be available irregularly and at much broader intervals (e.g., ever 15 minutes).